31 Nordic Geological Winter Meeting,Jan. 8-10, 2014. Abstract volume p. 72. Roaldset et al: Investigations of the kaolinite group minerals from in-situ weathered anorthosite at Dydland near Flekkefjord, SW Norway, show the presence of the polymorphs nacrite and/or dickite in addition to kaolinite. The kaolin deposits here were exploited for industrial purposes in the years 1898-1904. Reusch (1901) described the isolated areas of kaolinitic material and interpreted them to be of hydrothermal origin, while they, in the light of today’s geological knowledge, most probably are remnants of preglacial weathering. The basement rocks here are of Proterozoic age, while the time of the deep weathering is difficult to assess. Through geologic eras the region has been subjected to subsidence, sedimentation, uplift, fluvial and glacial erosion. In the Cenozoic the region experienced extensive tectonic movements. The Dydland site is close to the Skagerrak coast and lies about 100 m a.s.l. Detailed mineralogical studies of the Dydland kaolin by XRD, SEM-EDS, TEM and IR are in progress. Verification and characteristics of the kaolinite, dickite and/or nacrite will be presented and discussed in relation to origin and age. Diagenetic mineral transformations may indirectly give information about thickness of a post-weathering sedimentary cover later removed by erosion. Reference: Reusch, H. (1901) En forekomst af kaolin og ildfast ler ved Dydland nær Flekkefjord. Norges geologiske undersøkelse, 32, 99-103.

PRODUCTS OF PRE-GLACIAL WEATHERING ONSHORE NORWAY Elen Roaldset Natural History Museum, University of Oslo, Box 1172 Blindern, 0318 Oslo This presentation include a brief review of how our understanding of the weathering conditions that prevailed in Norway before the Quaternary glaciations, gradually has developed. Despite the effects of the glaciations are important features in the landscape, the preglacial topography has scarcely been destroyed to such an extent that it is unrecognizable. This view was already ascertained by Reusch and Brøgger in 1878, and supported by others (i.e. Nansen 1922,1927). Their successors neglected this view without any further investigations, and interpreted the pockets and smaller areas of weathered rocks to be of Quaternary origin, and the kaolinite occurrences to be of hydrothermal origin. Even V. M. Goldcmidt (1954) advocated that the fine-sediments in Scandinavia represented unweathered, mechanically crushed-up bedrock. He analyzed samples of these sediments in order to obtain an average analysis of the underlying bedrock. In the 1970-ies several studies of glacial sediments, bulk and fractions, and of underlying bedrock in the Numedal area, documented that mineralogical and chemical changes had occurred. Not until then was it realized that the glacial deposits was composed of glacially abraded material intermixed with older, preglacial weathered material. Compared to the bedrock, the heavy mineral content of the silt fractions of tills is reduced by approximately 50 %, and maghaemite, not at all observed in the crystalline rocks, but frequently occurring in tropical and sub-tropical lateritic soils, is a common heavy mineral. Other indications of intense weathering are quarts enrichments, amount of elements adsorbed on clays, occurrences of kaolinite and gibbsite, boulders of same kind as underlying bedrock. Conditions favourable for formation of maghaemite in soils have not persisted in Northern Europe since Tertiary (Miocene), while the weathering to gibbsite may be considerably older. Information sought outside the Norwegian mainland, i.e. the North Sea, and Northern Europe (including Southern Sweden), indicates several warm and humid periods through the Paleozoic and Mesozoic Eras. An interesting question is to which extent the weathered remnants have been protected against erosion by overlying sediments. Signs of compaction and early diagenesis can be traced. Further detailed mineralogical investigations may shed light on this.